The fluid dynamics and heat transfer phenomena acting on a generator rotor while operating at running speed are critical to the performance of a generator, in particular, air cooled rotors. The fluid dynamics and heat transfer phenomena, however, are by their nature exceedingly complex. For this reason, it has been a major engineering challenge to accurately calculate and predict rotor field winding operating temperatures. The determination and control of rotor field winding operating temperatures are crucial to generator efficiency and insulation system integrity.
Historically, most rotor designs have incorporated a conservative rating versus cooling capacity. This was necessary, in part, because of the uncertainties related to ventilation and operating temperatures of rotors. New lines of air-cooled rotors, however, are designed with very little margin between predicted operating temperatures and the maximum temperature allowable for efficient operation. As a consequence, it has become necessary to perform extensive ventilation flow development testing on both actual rotors and laboratory models to effectively design rotor ventilation systems.
The results of such testing are used in the design and calibration of rotor ventilation systems. A new, very powerful analytical technique known as Computational Fluid Dynamics ("CFD") is also used in the testing process. CFD modeling is an effective tool for calculating expected flows in complex systems, such as generator rotors. The testing and CFD modeling is particularly useful for verifying that ventilation systems in prototype rotors function as they are intended to by design and for confirming the integrity of the manufacturing processes used in fabricating these systems.
As a consequence, obtaining accurate measurements of flow parameters which influence the efficiency of heat dissipation in the rotor field windings is the chief objective of ventilation flow development testing of rotors. Key flow parameters include: the total overall volume of flow being pumped through the rotor, the pressure and velocity associated with this flow, and the distribution of this flow in the rotor, both along the length of the rotor body (axial), and around the rotor body shaft (circumferential). Known tests produce accurate representations of the axial flow distribution in a rotor, but they provide no information of the circumferential distribution of the flow. Thus, a need exists for a testing method and apparatus which can obtain an accurate measurement of circumferential flow distributions in a rotor.